On the sources of the height-intelligence correlation: new insights from a bivariate ACE model with assortative mating

Possible influence of sex on the relationship between dual-task gait costs and cognitive decline in older adults

The impact of cognitive decline in older adults can be evaluated with dual-task gait (DTG) testing in which a cognitive task is performed during walking, leading to increased costs of gait. Previous research demonstrated that higher DTG costs correlate with increasing cognitive deficits and with age. The present study was conducted to explore whether the relationship between the DTG costs and cognitive abilities in older individuals is influenced by sex differences. To address this objective, we conducted a study with 216 elderly participants (age range: 60 to 75 years, 127 females). These underwent Cognitive Functional Dementia (CFD) testing to determine their cognitive abilities and DTG testing to evaluate their gait parameters (gait speed, cadence, stride length, stride variance, and stance phase duration) while performing a backward serial number counting task. We carried out a correlation analysis between the CFD scores and the DTG costs. The DTG costs were calculated as the percentage difference between the gait parameters in single- and in dual-task testing, and the effects were compared considering the factors of sex and age. A significant negative correlation between the CFD scores and the dual-task costs of gait parameters was found only in males. The DTG costs did not differ between the sexes, while women obtained superior scores in the CFD test. The higher DTG costs significantly correlated with older age in men. In summary, our study provides evidence that, unlike in women, the DTG costs during the backward serial number counting task significantly increase in older men, correlating with declines in cognitive performance and increasing age. These findings suggest that the assessment of DT gait characteristics in relation to cognitive decline in older adults may manifest differently between sexes.

The relationship between the food intake frequency, weight status and intelligence in school children

This study aimed to explore the relationship between food intake frequency, weight status, and intelligence among school children. A cross-sectional study involved 562 children (aged 6.3-12.7 years) randomly selected from five elementary schools in Taichung City, Taiwan. Demographic information was collected, and the children's body weight and height were measured to calculate their body mass index. A food frequency questionnaire assessed the participating children's dietary habits. Intelligence quotient scores were evaluated using Raven's colored progress matrices for first and second graders, and Raven's standard progressive matrices for third to sixth graders. This study found that there was no significant relationship in intelligence quotient scores between gender, birth order groups, and weight status. The higher consumption of pork liver, hamburgers, fruit juices, and the Taiwanese snack "Science Noodles" was associated with lower intelligence quotient scores among school children.

Height and cognitive assessments in a cohort of US schoolchildren, kindergarten through fifth grade

An oft-repeated finding in child development research is that height and cognitive ability are positively related. Much of this work is limited in its ability to track height and cognitive development over time, with key constraints being the availability of longitudinal data and measures of ability that are comparable over time. This study evaluates the associations between height and assessments of reading, math, and science in a representative sample of US schoolchildren followed from kindergarten through fifth grade. Associations between height and assessment scores at each grade level, and height-growth and changes in scores over grade levels, are examined. The results suggest modest associations between concurrent height and assessment scores at each grade level that are robust to socioeconomic and school controls. There is limited association between height-growth and assessment outcomes, which is shown only for females. There is also little indication that height or height-growth is associated with improvements in scores. The findings suggest a modest association between height and cognitive ability in contemporary US schoolchildren, being attributed mostly to growth before kindergarten. The findings are consistent with the view that social and biological forces in early-life facilitate both physical and cognitive development.

The relationship between food habits and physical activity and the IQ of primary school children

BACKGROUND

Children's intelligence quotient (IQ) is influenced by various environmental and genetic variables. The current study aimed to determine how children's dietary choices and physical activity levels correlated with their IQ.

METHODS

A total of 190 students (111 girls and 79 boys) between the ages of 8 and 10 were chosen randomly for this cross-sectional research. For all children, questionnaires were utilized to gather information on their anthropometry, socio-economic position, food habits, and 24-h memory. Children's physical activity questionnaire (CPAQ) was also used to gauge their level of physical activity. Raven's color progressive intelligence test was also used to gauge children's IQ. All the questions may be filled out online with the assistance of parents. SPSS software was used to gather and evaluate the generated data.

RESULTS

Of 190 respondents, 79 (41.6%) are males, and 111 (58.4%) are girls. The results of the study showed that, a positive correlation between children's IQ and physical activity (P = 0.017, r = 0.17), if this relationship was not seen by gender. In addition, a positive correlation was observed between the IQ and food habits scores in all children (P = 0.001, r = 0.24), as well as by gender, that is, male (P = 0.04, r = 0.23) and female (P = 0.006, r = 0.26), which indicates that children with better food habits were associated with higher IQ.

CONCLUSION

It was shown that elementary school children's IQ, food habits, and degree of physical activity are all positively correlated.

Inverse Association between Educational Status and Coronary CT Calcium Scores: Should We Reflect This in Our ASCVD Risk Assumptions?

Education is not a factor included in most cardiovascular risk models, including SCORE2. However, higher education has been associated with lower cardiovascular morbidity and mortality. Using CACS as a proxy for ASCVD, we studied the association between CACS and educational status. Subjects, aged 40-69, from the Paracelsus 10,000 cohort, who underwent calcium scoring as part of screening for subclinical ASCVD, were classified into low, medium, and high educational status using the Generalized International Standard Classification of Education. CACS was dichotomised as either 0 or >0 for logistic regression modelling. Our analysis showed that higher educational status was associated with higher odds for 0 CACS (aOR 0.42; 95%CI 0.26-0.70; p = 0.001). However, there was no statistically significant association between the levels of total, HDL or LDL cholesterol and educational status, nor any statistical differences in HbA1c. SCORE2 did not differ between the three educational categories (4 ± 2% vs. 4 ± 3% vs. 4 ± 2%; p = 0.29). While our observations confirmed the relationship between increased educational status and lower ASCVD risk, the effect of educational status was not mediated via its impact on classical risk factors in our cohort. Thus, perhaps educational status should be taken into account to more accurately reflect individual risk in cardiovascular risk models.

The association between saving disposition and financial distress: A genetically informed approach

Saving disposition, the tendency to save rather than consume, has been found to be associated with economic outcomes. People lacking the disposition to save are more likely to experience financial distress. This association could be driven by other economic factors, behavioral traits, or even genetic effects. Using a sample of 3,920 American twins, we develop scales to measure saving disposition and financial distress. We find genetic influences on both traits, but also a large effect of the rearing family environment on saving disposition. We estimate that 44% of the covariance between the two traits is due to genetic effects. Saving disposition remains strongly associated with lower financial distress, even after controlling for family income, cognitive ability, and personality traits. The association persists within families and monozygotic twin pairs; the twin who saves more tends to be the twin who experiences less financial distress. This result suggest that there is a direct association between saving disposition and financial distress, although the direction of causation remains unclear.

Partner choice, confounding and trait convergence all contribute to phenotypic partner similarity

Partners are often similar in terms of their physical and behavioural traits, such as their education, political affiliation and height. However, it is currently unclear what exactly causes this similarity-partner choice, partner influence increasing similarity over time or confounding factors such as shared environment or indirect assortment. Here, we applied Mendelian randomization to the data of 51,664 couples in the UK Biobank and investigated partner similarity in 118 traits. We found evidence of partner choice for 64 traits, 40 of which had larger phenotypic correlation than causal effect. This suggests that confounders contribute to trait similarity, among which household income, overall health rating and education accounted for 29.8, 14.1 and 11.6% of correlations between partners, respectively. Finally, mediation analysis revealed that most causal associations between different traits in the two partners are indirect. In summary, our results show the mechanisms through which indirect assortment increases the observed partner similarity.

Weakening of the cognition and height association from 1957 to 2018: Findings from four British birth cohort studies

Background

Taller individuals have been repeatedly found to have higher scores on cognitive assessments. Recent studies have suggested that this association can be explained by genetic factors, yet this does not preclude the influence of environmental or social factors that may change over time. We thus tested whether the association changed across time using data from four British birth cohorts (born in 1946, 1958, 1970, and 2001).

Methods

In each cohort height was measured and cognition via verbal reasoning, vocabulary/comprehension, and mathematical tests; at ages 10/11 and 14/17 years (N=41,418). We examined associations between height and cognition at each age, separately in each cohort, and for each cognitive test administered. Linear and quantile regression models were used.

Results

Taller participants had higher mean cognitive assessment scores in childhood and adolescence, yet the associations were weaker in later (1970 and 2001) cohorts. For example, the mean difference in height comparing the highest with lowest verbal cognition scores at 10/11 years was 0.57 SD (95% CI = 0.44-0.70) in the 1946 cohort, yet 0.30 SD (0.23-0.37) in the 2001 cohort. Expressed alternatively, there was a reduction in correlation from 0.17 (0.15-0.20) to 0.08 (0.06-0.10). This pattern of change in the association was observed across all ages and cognition measures used, was robust to adjustment for social class and parental height, and modeling of plausible missing-not-at-random scenarios. Quantile regression analyses suggested that these differences were driven by differences in the lower centiles of height, where environmental influence may be greatest.

Conclusions

Associations between height and cognitive assessment scores in childhood-adolescence substantially weakened from 1957-2018. These results support the notion that environmental and social change can markedly weaken associations between cognition and other traits.

Funding

DB is supported by the Economic and Social Research Council (grant number ES/M001660/1); DB and LW by the Medical Research Council (MR/V002147/1). The Medical Research Council (MRC) and the University of Bristol support the MRC Integrative Epidemiology Unit [MC_UU_00011/1]. NMD is supported by an Norwegian Research Council Grant number 295989. VM is supported by the CLOSER Innovation Fund WP19 which is funded by the Economic and Social Research Council (award reference: ES/K000357/1) and Economic and Social Research Council (ES/M001660/1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Nutrition within the household: 18th through early 20th century female and male statures

When other measures for material conditions are scarce or unreliable, the use of height is now common to evaluate economic conditions during economic development. However, throughout US economic development, height data by gender have been slow to emerge. Throughout the late 19th and early 20th centuries, female and male statures remained constant. Agricultural workers had taller statures than workers in other occupations, and the female agricultural height premium was over twice that of males. For both females and males, individuals with fairer complexions were taller than their darker complexioned counterparts. Gender collectively had the greatest explanatory effect associated with stature, followed by age and nativity. Socioeconomic status and birth period had the smallest collective effects with stature.

Do blind people share the tall-man stereotype?

The stereotype of a tall man has been reported in numerous studies. High stature is commonly associated with advantages such as leadership skills, wealth, intelligence or social status, and actual differences between the short and the tall men were indeed found for these traits, mainly in favor of the tall men. It is not certain, however, whether the height-related effects are biologically determined or if they result from socially-driven mechanisms. In this study we wanted to explore whether congenitally blind individuals, who are unable to perceive other people’s stature through the most salient, visual channel, share the positive, height-related stereotype. Thirty-four congenitally blind and forty-three sighted men and women rated four positive characteristics of a tall or a short man. It was found that none of the traits assigned to the tall man by the sighted people was assigned to this person by the blind individuals. In the congenitally blind group, no differences between the assessments of the tall and the short man were revealed. We discuss our findings in the context of social perception and stereotypes research.

Avoiding dynastic, assortative mating, and population stratification biases in Mendelian randomization through within-family analyses

Estimates from Mendelian randomization studies of unrelated individuals can be biased due to uncontrolled confounding from familial effects. Here we describe methods for within-family Mendelian randomization analyses and use simulation studies to show that family-based analyses can reduce such biases. We illustrate empirically how familial effects can affect estimates using data from 61,008 siblings from the Nord-Trøndelag Health Study and UK Biobank and replicated our findings using 222,368 siblings from 23andMe. Both Mendelian randomization estimates using unrelated individuals and within family methods reproduced established effects of lower BMI reducing risk of diabetes and high blood pressure. However, while Mendelian randomization estimates from samples of unrelated individuals suggested that taller height and lower BMI increase educational attainment, these effects were strongly attenuated in within-family Mendelian randomization analyses. Our findings indicate the necessity of controlling for population structure and familial effects in Mendelian randomization studies.

Influence of height on likelihood of employment, occupational sorting, and earnings in 27 post-communist countries

OBJECTIVES

We study the influence of height on labour market outcomes using micro-data from a recent survey that cover 27 post-communist countries. Specifically, we focus on the influence of height on three dimensions of labour market outcome: (1) likelihood of employment, (2) occupational sorting, and (3) earnings.

METHODS

We use micro-data from 2016 Life-In-Transition survey (LITS) which was jointly conducted by the European Bank for Reconstruction and Development and the World Bank. We run several types of regression to show how height influences (1) likelihood of employment, (2) occupational sorting, and (3) earnings.

RESULTS

When controlling for a comprehensive set of covariates, for each 10 cm increase in height, the probability of getting a job increases by 1% points for males and by 3 for females. Equally, for each 10 cm increase in height, the probability of getting a job increases by 2% points in urban areas and rural areas. Our findings demonstrate that taller women and men are more likely: (a) being an employer rather than an employee; (b) to be employed in higher-paid and more prestigious sectors of finance, insurance, and real estate; (c) to be employed in private enterprises. Finally, when occupational sorting and socio-demographics are controlled for, a 10 cm increase in height results in a 5% increase in earning for men, and a 12% increase in earnings for women.

CONCLUSIONS

Using a diverse sample of 27 post-communist countries, we found that taller individuals have better labour market outcomes in terms of employment, occupational sorting, and earnings.

Body height in young adult men and risk of dementia later in adult life

This study examined the relationship between body height and dementia and explored the impact of intelligence level, educational attainment, early life environment and familial factors. A total of 666,333 men, 70,608 brothers, and 7388 twin brothers born 1939-1959 and examined at the conscript board were followed in Danish nationwide registers (1969-2016). Cox regression models were applied to analyze the association between body height and dementia. Within-brothers and within-twin pair analyses were conducted to explore the role of shared familial factors including partly shared genetics. In total, 10,599 men were diagnosed with dementia. The association between one z-score difference in body height and dementia (HR: 0.90, 95% CI: 0.89;0.90) was inverse and weakened slightly after adjustment for intelligence test scores and educational level. The associations persisted in within-brother analysis and revealed a stronger, but less precise, point estimate than the cohort analysis of brothers. The twin analysis showed similar, but imprecise estimates.

The relationship between height and leadership: Evidence from across Europe

To better explicate the well-researched finding that taller individuals have higher wages on average, potential mechanisms should be studied in detail. The present analysis investigates the relationship between height and the probability of being in a leadership position in the workplace using multinational European Social Survey data from 19 countries. Studying full-time, employed individuals between 20 and 55 years of age reveals considerable country differences which is beneficial for the estimated multilevel models as variation is increased. The results indicate a statistically significant effect whereby women are 0.15 percentage points more likely to be in a leadership position for each additional centimetre of absolute height when controlling for education and occupational position whereas there is no effect for men. In order to study the relevance of absolute vs relative height, which is the difference to the local peer-group, regional data is utilized. The main findings are that there is no effect of relative height for men but a statistically significant effect for women. For them, absolute and relative effects are about equally strong.

The causal influence of brain size on human intelligence: Evidence from within-family phenotypic associations and GWAS modeling

There exists a moderate correlation between MRI-measured brain size and the general factor of IQ performance (g), but the question of whether the association reflects a theoretically important causal relationship or spurious confounding remains somewhat open. Previous small studies (n < 100) looking for the persistence of this correlation within families failed to find a tendency for the sibling with the larger brain to obtain a higher test score. We studied the within-family relationship between brain volume and intelligence in the much larger sample provided by the Human Connectome Project (n = 1,022) and found a highly significant correlation (disattenuated ρ = 0.18, p < .001). We replicated this result in the Minnesota Center for Twin and Family Research (n = 2,698), finding a highly significant within-family correlation between head circumference and intelligence (disattenuated ρ = 0.19, p < .001). We also employed novel methods of causal inference relying on summary statistics from genome-wide association studies (GWAS) of head size (n ≈ 10,000) and measures of cognition (257,000 < n < 767,000). Using bivariate LD Score regression, we found a genetic correlation between intracranial volume (ICV) and years of education (EduYears) of 0.41 (p < .001). Using the Latent Causal Variable method, we found a genetic causality proportion of 0.72 (p < .001); thus the genetic correlation arises from an asymmetric pattern, extending to sub-significant loci, of genetic variants associated with ICV also being associated with EduYears but many genetic variants associated with EduYears not being associated with ICV. This is the pattern of genetic results expected from a causal effect of brain size on intelligence. These findings give reason to take up the hypothesis that the dramatic increase in brain volume over the course of human evolution has been the result of natural selection favoring general intelligence.

Body mass index and height in 11- to 16-year-old Austrian students attending two different school types with divergent socioeconomic backgrounds

Background

In developed countries high socioeconomic status (SES) is associated with lower body mass index (BMI) and greater height compared with low SES.

Aim

To investigate differences in BMI/height in adolescent students from two different school types with divergent SES backgrounds.

Methods

A total of 4579 students (2313 female), aged 11–16 years, attending either low SES vocation-directed secondary schools (VSS) or high SES secondary academic schools (AHS) were compared. Potential differences were investigated using ANCOVA models including sex, school type, geographical region and degree of urbanicity.

Results

At all ages between 11 and 16 years the BMI of students attending VSS was significantly higher than that of students attending AHS (mean +0.87kg/m²). The AHS students were on average taller (mean +0.93cm; p<0.001), without statistically significant age-specific differences. The taller height contributed to lower BMI by approximately 25%. Short stature, overweight and obesity were 2.3-fold, 1.8-fold and 2.5-fold, respectively more frequent in VSS than in AHS students. The BMI was higher in students in Vienna than in communities with >100,000 (p<0.001) and 20,000-100,000 (p=0.045) but similar to communities with <20,000 inhabitants.

Conclusion

These findings suggest that differences in BMI and height between students reflect early SES-based grouping into school types according to the academic level of the schools they attend.

The accuracy of LD Score regression as an estimator of confounding and genetic correlations in genome-wide association studies

To infer that a single-nucleotide polymorphism (SNP) either affects a phenotype or is linkage disequilibrium with a causal site, we must have some assurance that any SNP-phenotype correlation is not the result of confounding with environmental variables that also affect the trait. In this study, we study the properties of linkage disequilibrium (LD) Score regression, a recently developed method for using summary statistics from genome-wide association studies to ensure that confounding does not inflate the number of false positives. We do not treat the effects of genetic variation as a random variable and thus are able to obtain results about the unbiasedness of this method. We demonstrate that LD Score regression can produce estimates of confounding at null SNPs that are unbiased or conservative under fairly general conditions. This robustness holds in the case of the parent genotype affecting the offspring phenotype through some environmental mechanism, despite the resulting correlation over SNPs between LD Scores and the degree of confounding. Additionally, we demonstrate that LD Score regression can produce reasonably robust estimates of the genetic correlation, even when its estimates of the genetic covariance and the two univariate heritabilities are substantially biased.

Two by two, inch by inch: Height as an indicator of environmental conditions during childhood and its influence on earnings over the life cycle among twins

Adult height is a function of genetic predispositions and environmental influences during childhood. Hence, any variation in height among monozygotic twins, who share genetic predispositions, is bound to reflect differences in their environmental exposure. Therefore, a height premium in earnings among monozygotic twins also reflects such exposure. In this study, we analyze the height premium over the life cycle among Swedish twins, 10,000 of whom are monozygotic. The premium is relatively constant over the life cycle, amounting to 5-6% higher earnings per decimeter for men and less for women, suggesting that environmental conditions in childhood and youth affect earnings over most of the adult life course. The premium is larger below median height for men and above median height for young women. The estimates are similar for monozygotic and dizygotic twins, indicating that environmentally and genetically induced height differences are similarly associated with earnings.

The Effect of Schooling on Mortality: New Evidence From 50,000 Swedish Twins

By using historical data on about 50,000 twins born in Sweden during 1886-1958, we demonstrate a positive and statistically significant relationship between years of schooling and longevity. This relation remains almost unchanged when exploiting a twin fixed-effects design to control for the influence of genetics and shared family background. This result is robust to controlling for within-twin-pair differences in early-life health and cognitive ability, as proxied by birth weight and height, as well as to restricting the sample to MZ twins. The relationship is fairly constant over time but becomes weaker with age. Literally, our results suggest that compared with low levels of schooling (less than 10 years), high levels of schooling (at least 13 years of schooling) are associated with about three years longer life expectancy at age 60 for the considered birth cohorts. The real societal value of schooling may hence extend beyond pure labor market and economic growth returns. From a policy perspective, schooling may therefore be a vehicle for improving longevity and health, as well as equality along these dimensions.

Associations among height, body mass index and intelligence from age 11 to age 78 years

Background

Intelligence is related to both height and body mass index (BMI) at various stages of life. Several studies have demonstrated longitudinal relationships between these measures, but none has established whether height and intelligence, or BMI and intelligence are linked from childhood through to older age.

Methods

We assessed the relations between these measures over an interval of up to 67 years using data from the 36-Day Sample, an initially-representative sample of Scottish people born in 1936, assessed at age 11 years (N = 6,291) and again at 77–78 years (N = 722). This paper focuses on the 423 participants (6.7 % of the original sample) who provided relevant data in late adulthood.

Results

Height and intelligence were significantly positively associated in childhood (β = .23) and late adulthood (β = .21–.29). Longitudinal correlations also showed that childhood intelligence predicted late-adulthood height (β = .20), and childhood height predicted late-adulthood cognitive ability (β = .12–.14). We observed no significant relationship between BMI and intelligence either in childhood or in late adulthood, nor any longitudinal association between the two in this sample.

Conclusions

Our results on height and intelligence are the first to demonstrate that their relationship spans almost seven decades, from childhood through to late adulthood, and they call for further investigation into the mechanisms underlying this lifelong association.

Electronic supplementary material

The online version of this article (doi:10.1186/s12877-016-0340-0) contains supplementary material, which is available to authorized users.

HEIGHT, PARTNERS AND OFFSPRING: EVIDENCE FROM TAIWAN

Using Taiwanese data, this study finds that tall males are more successful in mate selection and reproduction, but the results are weakly significant. Height is not helpful for females’ reproductive success. Specifically, tall males are more likely to have a partner at present or in the past, have at least one child, have more children, have a shorter period of celibacy and have a longer time duration of living with a partner in their lifetime. Using mediation analysis, the study shows that tall males’ reproductive success is not due to their achievements in the labour market (earnings), but is simply due to their heightper se. Finally, a college student data set is used to explore the relation between height and dating hours. Tall male students have more dating hours, but no relation is found between females’ height and dating hours.

Height, aging and cognitive abilities across Europe

Previous research has found that as a marker of childhood circumstances, height is correlated with cognitive functioning at older ages. Using data from the Survey of Health, Ageing, and Retirement in Europe (SHARE) and about 17,000 respondents from 11 countries, we find that height is positively and significantly associated with cognitive functioning in later life despite controlling for a myriad of possible confounding factors. A 10 cm increase in height is associated with a 0.04 standard deviation increase in a summary cognitive score (mean 0.02, std. dev. 0.77). We find that being born in a country where the infant mortality rate at the time of birth is high has a negative and significant influence on cognitive functioning in later life. A 10% increase in the infant mortality rate is associated with a 0.1 standard deviation decrease in the summary cognitive score. We also find some evidence that height serves as a protective factor against age related deterioration in cognitive functioning. For persons of average stature, age related decreases in cognition scores are 3-5 percentage points smaller if they move up a quartile in the height distribution. Our results also suggest that there is a significant positive association between height and cognitive abilities across countries for this pre-1950 birth cohort of respondents, with correlations ranging from 0.4 to 0.8.

Some evidence for health-related marriage selection

OBJECTIVES

Married people live longer and are healthier than unmarried people. This can be explained in terms of marriage protection and marriage selection. The aim of the present study was to examine the direct effect of marriage selection on health status.

METHODS

Data were collected from the archives of the Lower Silesian Medical Center (DOLMED) in Wrocław, Poland. The sample consisted of 2,265 adult (never married or currently married) men. Subjects were assigned to categories for selected variables, including age, level of education, military category upon conscription, height, hearing acuity, and visual acuity. Military category, objective data gathered upon military conscription at age 18, was used to assess initial health status. To identify any relationships between marital status and health status, generalized linear models with binomially distributed dependent variable were used.

RESULTS

The never-married subjects were more likely to have been assigned to lower military categories, which indicates that their health status at age 18 was inferior to those conscripts who would later marry. Hearing acuity and visual acuity were generally worse in never-married subjects than in married subjects. Never-married subjects were also more likely to be short and less likely to be tall.

CONCLUSIONS

The results provide evidence for direct health-related marriage selection in men between 25 and 60 years of age. Poor health status reduces the likelihood of marriage.

Common genetic variants explain the majority of the correlation between height and intelligence: the generation Scotland study

Greater height and higher intelligence test scores are predictors of better health outcomes. Here, we used molecular (single-nucleotide polymorphism) data to estimate the genetic correlation between height and general intelligence (g) in 6,815 unrelated subjects (median age 57, IQR 49–63) from the Generation Scotland: Scottish Family Health Study cohort. The phenotypic correlation between height and g was 0.16 (SE 0.01). The genetic correlation between height and g was 0.28 (SE 0.09) with a bivariate heritability estimate of 0.71. Understanding the molecular basis of the correlation between height and intelligence may help explain any shared role in determining health outcomes. This study identified a modest genetic correlation between height and intelligence with the majority of the phenotypic correlation being explained by shared genetic influences.

The genetic correlation between height and IQ: shared genes or assortative mating?

Traits that are attractive to the opposite sex are often positively correlated when scaled such that scores increase with attractiveness, and this correlation typically has a genetic component. Such traits can be genetically correlated due to genes that affect both traits ("pleiotropy") and/or because assortative mating causes statistical correlations to develop between selected alleles across the traits ("gametic phase disequilibrium"). In this study, we modeled the covariation between monozygotic and dizygotic twins, their siblings, and their parents (total N = 7,905) to elucidate the nature of the correlation between two potentially sexually selected traits in humans: height and IQ. Unlike previous designs used to investigate the nature of the height-IQ correlation, the present design accounts for the effects of assortative mating and provides much less biased estimates of additive genetic, non-additive genetic, and shared environmental influences. Both traits were highly heritable, although there was greater evidence for non-additive genetic effects in males. After accounting for assortative mating, the correlation between height and IQ was found to be almost entirely genetic in nature. Model fits indicate that both pleiotropy and assortative mating contribute significantly and about equally to this genetic correlation.

Genetic and environmental influences on the relationship between flow proneness, locus of control and behavioral inhibition

Flow is a psychological state of high but subjectively effortless attention that typically occurs during active performance of challenging tasks and is accompanied by a sense of automaticity, high control, low self-awareness, and enjoyment. Flow proneness is associated with traits and behaviors related to low neuroticism such as emotional stability, conscientiousness, active coping, self-esteem and life satisfaction. Little is known about the genetic architecture of flow proneness, behavioral inhibition and locus of control--traits also associated with neuroticism--and their interrelation. Here, we hypothesized that individuals low in behavioral inhibition and with an internal locus of control would be more likely to experience flow and explored the genetic and environmental architecture of the relationship between the three variables. Behavioral inhibition and locus of control was measured in a large population sample of 3,375 full twin pairs and 4,527 single twins, about 26% of whom also scored the flow proneness questionnaire. Findings revealed significant but relatively low correlations between the three traits and moderate heritability estimates of .41, .45, and .30 for flow proneness, behavioral inhibition, and locus of control, respectively, with some indication of non-additive genetic influences. For behavioral inhibition we found significant sex differences in heritability, with females showing a higher estimate including significant non-additive genetic influences, while in males the entire heritability was due to additive genetic variance. We also found a mainly genetically mediated relationship between the three traits, suggesting that individuals who are genetically predisposed to experience flow, show less behavioral inhibition (less anxious) and feel that they are in control of their own destiny (internal locus of control). We discuss that some of the genes underlying this relationship may include those influencing the function of dopaminergic neural systems.

Correlation and Causation in the Study of Personality

Personality psychology aims to explain the causes and the consequences of variation in behavioural traits. Because of the observational nature of the pertinent data, this endeavour has provoked many controversies. In recent years, the computer scientist Judea Pearl has used a graphical approach to extend the innovations in causal inference developed by Ronald Fisher and Sewall Wright. Besides shedding much light on the philosophical notion of causality itself, this graphical framework now contains many powerful concepts of relevance to the controversies just mentioned. In this article, some of these concepts are applied to areas of personality research where questions of causation arise, including the analysis of observational data and the genetic sources of individual differences. Copyright © 2012 John Wiley & Sons, Ltd.

Height and cognitive achievement among Indian children

Taller children perform better on average on tests of cognitive achievement, in part because of differences in early-life health and net nutrition. Recent research documenting this height-achievement slope has primarily focused on rich countries. Using the India Human Development Survey, a representative sample of 40,000 households which matches anthropometric data to learning tests, this paper documents a height-achievement slope among Indian children. The height-achievement slope in India is more than twice as steep as in the U.S. An earlier survey interviewed some IHDS children's households eleven years before. Including matched early-life control variables reduces the apparent effect of height, but does not eliminate it; water, sanitation, and hygiene may be particularly important for children's outcomes. Being one standard deviation taller is associated with being 5 percentage points more likely to be able to write, a slope that falls only to 3.4 percentage points controlling for a long list of contemporary and early-life conditions.